Ion Energy Threshold in Low-Temperature Silicon Epitaxy for Thin-Film Crystalline Photovoltaics

Plasma-enhanced chemical vapor deposition (PECVD) enables epitaxial silicon deposition for up to several micrometers and at low temperatures (as low as 150 °C). We present herein a detailed study of the effect of ion energy at high (above 2 torr) and low (below 1 torr) pressure, where the plasma and surface reactions are expected to be different, i.e., driven, respectively, by high-order and low-order silane precursors. We find a sharp energy threshold at low pressure, above which no epitaxy can be obtained, but this threshold is relaxed at high pressure. The occurrence of epitaxy breakdown is studied and compared in detail for these two different pressure regimes.